1. Field of the Invention
The present invention relates to improvements in an optical scanning device for scanning a subject medium.
2. Description of the Related Art
In recent years, with development of digital techniques and light sources, numerous high performance printing equipment and the like have been developed, wherein a light beam modulated according to image signals scans a subject matter, such as photographic pictures and printed matter (which is hereafter referred to as a scanning subject medium), that is sensitive to light to record an image on a paper. In such a printing equipment, the utilization is made of an optical scanning device to scan a scanning subject medium. This optical scanning device is, for typical example, configured such that a laser beam from a laser diode is repeatedly reflected and deflected by a rotary polygon mirror and further directed as a scanning beam to a subject medium through an f-.theta. lens. Because deflection of the scanning beam by the polygon mirror causes defectiveness in the evenness of velocity of straight line motion of the scanning beam along a canning line on the scanning subject medium relative to a temporal change in rotational angle .theta. of the polygon mirror, the f-.theta. lens is employed. In order for the optical scanning device to avoid the defectiveness in the evenness of velocity of straight line motion of the scanning beam along a scanning line and keep the velocity of straight line motion of the scanning beam. As is known from, for example, Japanese Patent Publication No. 6-95176, the f-.theta. lenses that is installed in this type of optical scanning device comprises a plurality of lens elements.
In light of the tendency toward small and light equipment and instruments, for business use or for personal use, there is a strong demand for small and light printers and, in the nature of course, small and light optical scanning devices. It is been a matter of concern how to realize small and light printers and optical scanning devices.